Process of providing a thin coherent layer to a rough surface in a vessel



6 R 1 0R T 0 NH 6 E E 1 WP 00 I N 2 M JOHANNES DE GIER BY g: AGE/VT J. DE GIER ETAL PROCESS OF PROVIDING A THIN COHERENT LAYER "TO A ROUGH SURFACE IN A VESSEL Filed Apnl 30, 1948 Nov. 4, 1952 Paten ted Nov. 4, 1 952 *PROCESS OF PROVIDING A THIN connnnn'r -"LAYER'T0'A ROUGH SURFACE IN A VESSEL o, es "de"Giei and Jan Peper, Eindhoven, jNetherlaiijds, "assignors to Hartford National ns hi and Trust Company, Hartford, 061111., as

trustee --ADll.liafl0n;April 30, 1948, Serial N0,'24,126

" ln-the Netherlands June 2'7,- 1947 rentals. "(01. iiiass) This invention relates to a methddfof 'covei ing a rough surface i'nsidea vessel with a'thin, coherent layer-which doesn'ot substantiallypenetrate between the unevennesses'of the rough surface. The invention furthermore concerns vessels provided with such layers.

It is' frequently desirable that j'rou'gh' surfaces inside a vessel should be coated with a thin,""coherent layer'which shuts-off "such surfaces so as to render the latter substantially smooth. The term smooth? is to be understood in this case to mean that the material "of the coherent layer does not substantially penetrate between the unevenne'sses of the surface'and hence covers the latter in form of askin or foil.

As a first example, we may mentionhere socalled Dewar vessels. As is well-known, a portion'of the inner wall of sucha vessel'is covered with a reflecting metallic layer. "As a rule, such a metallic'layer is applied either by vaporisation of a certain amount of metal or by a chemical process, the amount of "metal required for obtaininga reflecting layer'varying with the roughness of the surface of the substratum, since it is evident that all unevennesses thereof "arerequired to be filled up before a coherent'metallic layer'may be ensured. lnorderflto utiliseaininimu'm amount ofrrietaLit is therefore desirable to make the substratum assmobth as possible'and this is a disadvantagefisince the working and the 'manufacture'of a vessel "is thus rendered more complicated and hence more expensive. It the unevennesses are preliminarily covered with a thin, coherent layer and themetal is applied thereto, the manufacture is rendered materially cheaper, if at least there isa simple methed for providingthe thin coherent layer. 1 In this caseit is' also possible to utilise more expensive metals on account of the small amount of metal required. g V

I A s'econdexamplein whicha thin, coherent layer is advantageously applied to a rough" surface is -a frosted incandescent lamp which is coherent layer. Thus, in the case of iconoscopes, the problem frequently arises that a granulous substratum of oxidised silver balls is required to be covered with a metallic layer to serve for 001- lectingsecondary electrons. In this case it is entirely impossible to utilise a thickness of layer such that all cavities and unevennesses between the grains are filled, since it must be possible for the primary electrons to penetrate through the metallic"layer,whereas the secondary electrons must be collected. If the oxidised silver grains are firstshut-off'by' a'sheet or foil, a thin metallic layer may be provided on this smooth surface in a simple manner. If desired, the foil may subsequently be removed.

Finally we may mention, as an example, the coating of luminescent screens in'electric dischargeft'ubes with a thinyrefieicting metallic layer. Suc'ha metallic mirror on a luminescent screen in a discharge tube is-already known. It serves to increase the amount of light radiated to the observer in the use of the tube. Since the metallic layer is required to be provided on the side adjacent the cathode,itis necessary that the electrons should be capable of penetrating throughthis layer. Consequently, a limitation is set to the choice of the thickness of the metallic layer. If the grains of luminescent ma-' terial are first covered by a thin, coherent layer in form of a sheet or foil which does not penetrate into the apertures between the grains, it is possible to provide on this "foil a very thin metallic layer of high reflecting power.

The use of an intermediate layer, for example of nitrocellulose, has previously been described for luminescent screens in Braun' tubes. Furthermore it has been described that this intermediatelayer may be removed afterwards, if desired.

The application of such a layer consisting, for example, of nitrocellulose involves several difliculties. One of these difficulties is that the material of theintermediate layer penetrates between the unevennesses to an inadmissible extent, so 'that smooth closurecannot beensured. Furthermore holes and cracks frequently arise in this coherent-layer.

A copending application Serial No. 763,243 filed July 24, 1947;describes a method in which attempts are made to mitigate the' above-mentioned disadvantages. In this method use is made of aliquid by whichthe cavities and unevennes'ses of a rough surface are first closed, the filling liquid beingsubsequently covered-by is removed. This method suffers from the dis- 3 advantage, however, that the amount of filling liquid is required to be dosed very accurately and this is often impossible.

The invention provides a new method of applying a thin, coherent layer which does not substantially penetrate between the unevennesses of the rough surface, which method mitigates the aforesaid disadvantages, is very simple and economical and ensures a surface of considerable smoothness.

In a method according to the invention, the coating of a rough surface inside a vessel with a thin, coherent layer which does not substantially penetrate between the unevennesses of the rough surface, is effected in the following manner. An amount of liquid is introduced into the vessel so that the rough surface is entirely submerged. n the surface of this liquid filling is brought a solution exhibiting a specific gravity lower than that of the liquid, of a larger amount of material of the coherent layer to be provided than that required for the formation of this layer, the vessel being subsequently tilted and the liquid decanted, followed by drying of the layer remaining on the rough surface and consisting of solvent and dissolved substance.

The thin, coherent layer is obtained in the method according to the invention during the tilting operation of the vessel, since then a separating line is produced between the rough surface and the solution of the material of the layer to be applied, which floats on the filling liquid. During the tilting movement of this separation line moves across the whole rough surface and on the latter remains a thin layer of the solution providing, by drying, a thin coherent sheet on the unevennesses.

With some shapes of vessels the dimculty is encountered that, if no particular steps were taken, the filling liquid and the solution floating thereon would flow too rapidly out of the vessel during the tilting operation. As a result thereof, the coating on a portion of the surface would be inferior to that of the rest. The particular steps to avoid this consist in closing the vessel, prior to tilting, by a stopper, which may be, for example, a cork or a rubber stopper. The stopper may be removed when the tilting movement has been performed completely. In a further embodiment the closing stopper may be provided with one or more apertures to allow the liquid to flow away. If desired, such apertures may temporarily be closed.

The filling liquid introduced into the vessel may be, for example, water and the coherent layer may be nitrocellulose. The nitrocellulose may be dissolved, for example, in butyl acetate or in a mixture consisting of butyl acetate and xylene. If necessary, a softening agent may be added to the solution.

v The method according to the invention is applicable to luminescent screens provided in an electric discharge tube in any arbitrary manner. It affords particular advantages, however, in the case of luminescent layers obtained by the socalled settling method, since in this method the electric discharge tube is filled with a filling liquid, for example water, in which the luminescent material is suspended and forms the luminescent material proper by settling. Hitherto, the filling liquid has been decanted subsequent to settling and the discharge tube worked further. The method according to the invention may be combined with this known method in a very simple method at the same time as a filling liquid for the provision of a thin, coherent layer.

Subsequent to the drying process, the sheet may be coated with a metallic mirror, a luminescent layer, or whatever maybe desired.

The tilting movement of the vessel preferably takes place in a regular way since a skin of uniform thickness is thus ensured.

"The invention will now be explained more fully by reference to the accompanying drawing illustrating, by way of example, a number of phases of the coating process of a luminescent screen provided on the bottom of a Braun tube of ordinary shape, that is to say constituted by a conical portion and an adjoining cylindrical neck.

In the drawing, Figure 1 illustrates the moment at which the process according to the invention is started. Figures 2, 3 and 4 illustrate successively the steps taken in tilting the tube, during which operation the neck is closed by an apertured stopper.

Figure 1 shows the bottom I of the conical part of the Braun tube, which is covered with the luminescent layer 2, obtained, for example, by settling from the layer of filling liquid 3 (consisting, for example, of water). On the layer 3 is poured a layer 4 of a solution of nitrocellulose in a mixture consisting, for example, of butyl acetate and xylene. The amount of nitrocellulose in this solution is materially greater than that required to cover the surface of the luminescent layer 2 with a, thin, coherent and smooth layer of nitrocellulose. When the solution has been introduced, the neck of the Braun tube is closed by a rubber stopper 5, in which are two glass tubes 6 and l. The glass tube- 6 serves to allow the liquid to flow out in tilting the tube, whereas the tube I serves to allow the penetration of air. Figure 2 shows a position in which the Braun tube is tilted by approximately 45 about an axis located approximately on the separation between the neck and the conical part. The liquid level has now reached the position as shown, whereas it was initially in the position indicated by. the dotted line 8. The separating line between the level of the liquid and the wall of the tube in tilting the tube has been displaced from point 9 to point [0. During this motion a thin layer consisting of nitro-cellulose and a little solvent has remained on the portion ll of the tube Wall. Figure 3 shows a position of the tube after turning by approximately in which position half of the luminescent screen is already coated. The tube 1 serving to allow the penetration of air is still closed in this position so that the liquid cannot flow off through the tube 6. Only in the position after turning by as illustrated in Fig. 4 is the tube 1 opened with the result that the filling liquid and the solution of nitrocellulose floating thereon flows off. After removal of the stopper 5, the solvent is allowed to evaporate from the layer remaining on the rough surface. so as to form the thin, coherent sheet. It is evident that, after the 180 tilting operation and the flowing out of the liquid, 2. large portion of the conical part is covered with a thin layer. At the areas at which such a layer is undesired, it is removed, for example, by brushmg.

In this method it would alternatively be possible to utilise a stopper which is entirely closed and removed after turning by 180. It is more practical, however, to utilise an outlet tube and a tube for the penetration of air.

manner by using the filling liquid of the settling 7s The use Of a closing pper is desirable in atube of the shape as illustrated since otherwise in the position shown in Fig. 3, the liquid filling and the solution floating thereon would flow off with undue velocity, thus preventing the lower portion of the luminescent screen to be covered regularly. In other forms of discharge tubes, however, a stopper is not always required.

What we claim is:

1. The method of forming a coating on an interior rough surface of a vessel, comprising the steps of covering the surface to be coated with a liquid having a given specific gravity, depositing on the surface of the liquid a layer of a solution of acoating material relatively insoluble in the liquid and containing more coating material than that required to form the coating on the said surface, the solution of coating material having a specific gravity less than the specific gravity of the liquid whereby the solution of coating material floats as a layer on the surface of the liquid, tilting the vessel to progressively expose the liquid covered surface of the vessel to thereby deposit a coating of said solution on said surface, decanting the liquid and excess solution of coating material, and drying the so-formed coating on said rough surface.

2. The method of forming a coating on an interior rough surface of a vessel, comprising the steps of covering the surface to be coated with a liquid having a given specific gravity, depositing on the surface of the liquid a layer of a solution of a coating material relatively insoluble in the liquid and containing more coating material than that required to form the coating on the said surface, the solution of coating material having a specific gravity less than the specific gravity of the liquid whereby the solution of coating material floats as a layer on the surface of the liquid, inverting the vessel to progressively expose the liquid covered surface of the vessel to thereby deposit a coating of said solution on said surface, decanting the liquid and excess solution of coating material, and drying the so-formed coating on said rough surface.

3. The method of forming a coating on an interior rough surface of a vessel, comprising the steps of covering the surface to be coated with water, depositing on the surface of the water a layer of a solution of a coating material relatively insoluble in the liquid and containing more coating material'than that required to form the coatingon the said surface, the solution of coating material having a specific gravity less than the specific gravity of water whereby the solution of coating material floats as a layer on the surface of the water, tilting the vessel to progressively expose the water covered surface of the vessel to thereby deposit a coating of said solution on said surface, decanting the water and excess solution of coating material, and drying the so-formed coating on said surface.

4. The method of forming a coating on an interior rough surface of a vessel, comprising the steps of covering the surface to be coated with water, depositing on the surface of the water a layer of a solution of a coating material containing nitrocellulose and butyl acetate and containing more coating material than that required to form the coating on the said surface, tilting the vessel to progressively expose the water covered surface of the vessel to thereby deposit a coating of said solution on said surface, decanting the water and excess solution of coating material, and drying the so-formed coating on said rough surface.

5. The method of forming a coating on an interior rough surface of a vessel, comprising the steps of covering the surface to be coated with water, depositing on the surface of the water a layer of a solution of coating material containing nitrocellulose, butyl acetate, and Xylene and containing more coating material than that required to form the coating on the said surface, tilting the vessel to progressively expose the water covered surface of the vessel to thereby deposit a coating of said solution on said surface, decanting the Water and excess solution of coating material, and drying th so-formed coating 1 on said rough surface.

' 6. The method of forming a coating on an interior rough surface of a vessel, comprising the steps of covering the surface to be coated with water, depositing on the surface of the water a layer of a solution of a coating material containing nitrocellulose, butyl acetate and a softening agent and containing more coating material than that required to form the coating on the said surface, tilting the vessel to progressively expose the water covered surface of the vessel to thereby deposit a coating of said solution on said surface, decanting the water and excess solution of coating material, and drying the so-formed coating on said rough surface.

'7. The method of forming a coating on an interior rough surface of a vessel, comprising the steps of covering the surface to be coated with a liquid having a given specific gravity, depositing on the surface of the liquid a layer of a solution of a coating material which is relatively insoluble in the liquid and containing more coating material than that required to form the coating on the said surface, the solution of coatin material having a specific gravity less than the specific gravity of the liquid whereby the solution of coating material floats as a layer on the surface of the liquid, tilting the vessel to progressively expose the liquid coveredsurface of the vessel to thereby deposit a coating of said solution on said surface, decanting the liquid and excess solution formed coating.

of coating material, drying the so-formed coating on said rough surface, and evaporating a metal to deposit a metallic mirror on the so- JOHANNES DE GIER. JAN PEPER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE METHOD OF FORMING A COATING ON AN INTERIOR ROUGH SURFACE OF A VESSEL, COMPRISING THE STEPS OF COVERING THE SURFACE TO BE COATED WITH A LIQUID HAVING A GIVEN SPECIFIC GRAVITY, DEPOSITING ON THE SURFACE OF THE LIQUID A LAYER OF A SOLUTION OF A COATING MATERIAL RELATIVELY INSOLUBLE IN THE LIQUID AND CONTAINING MORE COATING MATERIAL THAN THAT REQUIRED TO FORM THE COATING ON THE SAID SURFACE, THE SOLUTION OF COATING MATERIAL HAVING A SPECIFIC GRAVITY LESS THAN THE SPECIFIC GRAVITY OF THE LIQUID WHEREBY THE SOLUTION OF COATING MATERIAL FLOATS AS A LAYER ON THE SURFACE OF THE LIQUID, TILTING THE VESSEL TO PROGRESSIVELY EXPOSE THE LIQUID 